It was seen at harvest time, occupying the entire northern side from the eastern corner to the western corner. Its form was as follows: a blood-red scepter, a green one, a black one, and a saffron-colored one. It was going from below to above. When one scepter was extinguished, another one went up. And when someone was looking at it, it was changed into seventy shapes.
“One of the most obvious scientific merits for doing this research is that we can confirm past extreme events,” said Hiroaki Isobe, an associate professor in the Graduate School of Advanced Integrated Studies in Human Survivability at Kyoto University. Isobe has collaborated with more than a dozen scientists and historians in searching and analyzing various archives for records of sightings in the heavens.
“For instance, in 775 and 994 there were sharp peaks in carbon-14 seen in tree rings, which is evidence of large amounts of cosmic rays in the atmosphere,” Isobe told Eos on Monday after he spoke at a joint conference of the Japan Geoscience Union (JpGU) and the American Geophysical Union (AGU) in Chiba, Japan.
“This tells you that cosmic rays were there, but not their origin, such as whether they were from extreme space weather or gamma ray bursts or supernovas. If we can find evidence of low-latitude auroras in the same year as these peaks, it strongly supports the hypothesis that this carbon-14 is due to strong solar activity.”
That the circa 771–772 auroras were visible from the relatively low geomagnetic latitude of eastern Turkey suggests they were associated with strong geomagnetic storms, according to Isobe. Although the Zūqnīn sketch was known to some historians, Isobe said his team is the first to investigate it in detail and confirm it was an aurora. Sketches are particularly useful in historical astronomy, he added, because words alone can be harder to interpret.
Written descriptions of auroras have been found in cuneiform clay tablets from Babylonia, whereas ancient Chinese and Japanese observers used terms such as “red vapor” or “white rainbow” to describe auroras. To determine whether a record really describes an aurora, features such as the time, moon phase, color, size, and direction, as well as other contemporary observations, must be taken into account. If the report was made during a full moon, for instance, it could be the result of atmospheric scattering of moonlight. But if it can be established that the phenomenon was an aurora, such records are also a record of solar activity.
“You can actively mine these archives, and there’s a huge treasure trove of information in them,” said Martin Connors, Canada Research Chair in Space Science, Instrumentation and Networking at Athabasca University in Alberta. “I think they’re being very careful about interpretation, such as using observations taken on a moonless night and correlating them with changing magnetic latitude.”
Ryuho Kataoka of Japan’s National Institute of Polar Research, one of Isobe’s collaborators and a fellow speaker at a space weather session of the JpGU-AGU conference, shared the results of a study showing that aurora sightings in Japan in 1204 were likely caused by significant magnetic storms resulting from multiple coronal mass ejections. He noted that the observations were made at Kyoto during a time when, because of the orientation of Earth’s magnetic field, the region was especially susceptible to geomagnetic effects. Kataoka showed attendees images of handwriting from the Meigetsuki (The Record of the Clear Moon), a diary written by Fujiwara no Teika, a poet-scholar who died around 1241.
“Their best events were when the northern latitude in Kyoto was most favorable for seeing them. That corroborates these reports being of aurora,” Connors said.
The Zūqnīn manuscript also contains a sketch of a comet plus a description that says the comet had two tails. The authors noted that the date coincides with the appearance of Halley’s Comet in May 760 and that it is known to have also been observed by Chinese astronomers. A simulation using astronomy software led the researchers to conclude that the Zūqnīn chronicle contains the earliest known description of two tails in a comet.
Isobe and his colleagues have published more than 10 papers about ancient records of celestial phenomena, including a January 2017 study about the aurora sketches in Publications of the Astronomical Society of Japan and a February 2017 study in Space Weather.